Vacuum interrupter or switch for electric power networks

ABSTRACT

A single-pole interupter, for a ower network, having a plurality of contact elements arranged to form in the open position a series of spaced interrupting gaps, each contact element being provided with screenin means for shielding these interrupting gaps from each other. Means are provided for preventing the sidcharge that occurs upon opening the interrupter from restarting once the current has passed through zero during the first change in alternation after the interrupter is opened.

VACUUM INTERRUPTER OR SWITCH FOR ELECTRICPOWER NETWORKS 7 Sheets-SheetFiled Dee. 15 1971 2 L?. A inv h il.

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Dec. 5, 1972 P, GEM-:QUAND 3,705,144

VACUUM INTERRUPTER 0R SWITCH Fon Emzcfrmc POWER NETWORKS Filed Dec. l15,1971 7 Sheets-Sheet 3 Dec. 5, 1972 P. GENEQUAND 3,705,144

VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Deo. l5,1971 '7 Sheets-Sheet L1 FIG. l2

De 5 1972 P. GENEQUAND l 3,705,144

VACUUM INTERRUPTER- OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Dec. 15,1971 I 7 sheets-sheet V5 w22 'l H3 F/Gf /4 i Y. 97A FIG /5 ZL/f De@ 5,1972 P. GENEQUAND VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWERNETWORKS Filed Dec. l5, 1971 7 Sheets-Sheet` 6 Dec' 5 1972 P. GENEQUAND3,705,144

VACUUM INTERRUPTER OR SWITCH FOR ELECTRIC POWER NETWORKS Filed Deo. l5,1971 '7 Sheets-Sheet 7 FIG. v I9 United States Patent() 3,705,144 VACUUM'INTERRUPIER OR SWITCH FOR ELECTRIC POWER NETWORKS Pierre Genequand,Geneva, Switzerland, assignor to Battelle Memorial Institute, Carouge/Geneva, Switzerland Filed Dec. 15, 1971, Ser. No. 208,209 Claimspriority, application Switzerland, Dec. 24, 1970, 19,029/70; Nov. 22,1971, 16,945/71 Int. Cl. H01h 33/ 66 U.S. Cl. 200-144 B 22 ClaimsABSTRACT F THE DISCLOSURE The invention relates to a vacuum single-poleinterrupter or switch for alternating electric current, having aplurality of contact elements operating in series, said contact elementsbelonging to first and second contact armatures capable of moving inrelation to each other along an axis of displacement, the contactelements of one armature cooperating with those of the other armature soas together to form a chain of contact elements constituting, when theinterrupter is closed, a conduction path alternately passing through thecontact elements of said two armatures and forming, when the interrupteris open, a series of interrupting gaps alternately deined by saidcontact elements, the two end elements of this chain being electricallyconnected to the one and the other, respectively of two terminals forconnection of this interrupter to an electrical network.

The problem of breaking a high voltage alternating current circuit haslong existed, particularly in grid systems. The problem consists inimparting to the medium in which the contact elements operate and inwhich ilashes the discharge resulting from a break, the ability torecover very quickly, after the current has dropped to zero, suflicientdielectric strength to enable a potential difference of some 100 kv. tobe set up across the contact elements without causing the discharge tobe restarted. In other words, it is the phenomenon of the dielectricrestoration of the medium in which the discharge flashes thatconstitutes one of the key elements of the problem.

Besides the solutions which consist in using a fluid under pressure(compressed air, oil, sulphur hexaiiuoride) for the medium and in whichdielectric restoration is dependent on the deionization mechanism,several solutions have been put forward in which the contact elementsare required to operate in a vacuum. The devices embodying thesesolutions are known as vacuum interrupters or switches. In interruptersof this type, dielectric restoration is dependent on the charge carriersand on the vapour issuing from the hot points of the cathode known ascathodic spots condensing on the walls adjacent the location where thedischarge took place and in particular on the contact elements per se.Since such condensation is all the faster when the surfaces on which ittakes place are more closely set together, vacuum interrupters arecharacterized by a small gap between the contact elements, of the orderof 1 cm. This provides substantial advantages as regards the controlmechanism since the 'ice latter is only required to move the contactelements over short distances. The forces of inertia to be overcome arethus small so that the vacuum interrupter can be made to operate withlittle noise.

With arcs in a vacuum, there exist two llow conditions for the currentdischarge, i.e. the diffuse arc flow conditions and the single columnflow conditions.

Under diluse arc ilow conditions, which obtain with small currents(intensities of less than 2 ka.), the current is conveyed by severalparallel conical columns, termed Reece cones, Whose apexes are locatedon the cathode and form the cathodic spots mentioned earlier. Thesecathodic spots move by sweeping across the cathode, somewhat like gasmolecules, at speeds of some 10 to m./s., and the corresponding Reececones, which have a very short life, something of the order of 1microsecond to 1 millisecond, keep going through subdivision. They eachconvey a current of not more than 30 to 100 a. Under these diffuse arcflow conditions, the cathode is subjected to little erosion, notexceeding 50 to 100 rtg/as.

Under single column ow conditions, the current is conveyed by a singlecolumn resulting from a regrouping of the Reece cones. This singlecolumn, which carries all of the current, has little mobility and as aresult causes destructive fusion of the contact elements. The moltenregions give rise to much evaporation of the metal, so that thedischarge comes to behave like a high pressure arc. Dielectricrestoration is then adversely affected and the discharge starts up againafter the current has dropped to zero. To increase cooling to preventfusion and hence to limit evaporation does not solve the problem. Thereason for this is that the heat conductivity of the metal from whichthe contact elements are made is such as not to enable the heatgenerated at the point of impact of the discharge to be removedsufficiently quickly. Since this point has very little mobility aconsiderable amount of power comes to be concentrated there. Attemptshave been made to compel the point of impact to move, as by subjectingthe discharge to a magnetic iield. There are for instance solutions inwhich the contact elements are divided up into curvilinear petals" byhelicoidal slots. The current is then compelled to follow within thecontact elements a spiral path and to generate as a result a magneticfield capable of moving the arc by electromagnetic interaction.Solutions of this kind are for instance described in U.S. Pats. Nos.3,210,505, 3,185,799, 3,185,- 798, 3,185,797, 3,089,936 and 2,949,520and in French Pat. No. 1,410,884. However, because of the resultingcomplex shape of the electrodes, these solutions are not sufficient toprevent the appearance of single column ow conditions when the currentincreases.

It has been shown by C. W. Kimblin (I. Appl. Phys. 40 (1969), p. 1744)that the appearance of single column ow conditions is linked with asubstantial increase in the anodic voltage drop, which can reach 100 v.or more, and that this effect becomes all the more marked when thecolumns of the diffuse arc are longer, such lengthening being equallywell due to the spacing between the contact elements and to the edgeeiect of the latter, i.e. the propensity of the discharge impact pointsto escape towards the edges of the contact elements.

Further, any interrupter, when open, must be able to withstanddisruption, i.e. to bear a high potential difference without anydischarge flashing across its contact elements. This is particular meansthat the medium between the contact elements must have high dielectricstrength and that the state of the surface of these elements must beexcellent. However, the best possible surface conditions are veryrapidly affected by the erosive action of the discharges occurring wheninterrupter is being opened. As for the dielectric strength of themedium, it is dependent on the pressure prevailing therein. Thispressure must remain such that the mean free path of a charged particlebe suiciently long to prevent this particle from being accelerated tothe point of generating an avalanche process (Paschen discharge). Thismeans that it is not enough simply to create once and for all a highvacuum in the space lying between the contact elements. It is alsonecessary to prevent the latter later from giving rise to too muchdegassing. Use is therefore made in making the contact elements of ultrapure metals, in particular of metals which have been purified by zonalfusion. The last resort for increasing voltage resistance consists inincreasing the distance between the electrodes. Now, breakdown voltageincreases linearly with distance only over distances of less than about10 mm. Over greater distances, the disruption voltage increasesproportionately with the square root of the distance, i.e. more slowly.When the voltage to be withstood exceeds several tens of kilovolts, theinterelectrode distance becomes large and this, lirstly, runs counter tomaintaining diffuse arc flow conditions when the contact elements arebeing opened and, secondly, makes it necessary to provide a powerful andnoisy actuating mechanism (to move the contact elements over a largedistance in a very short time). As a result, it has been proposed todivide the space between the contact elements into several partialspaces by arranging a chain of pairs of contact elements wherein thepairs are mounted in series relationship one after the other, each pairhaving at least one movable contact elements. Such arrangements are inparticular described in U.S. Patents Nos. 3,185,797, 3,185,798 and2,976,382, and-in an article by H. C. Ross entitled Vacuum SwitchProperties of Power Switching Applications published in Trans. AIEE 77(1958) p. 104-117.

Vacuum switch or interrupter designers thus have to contend with twocontradictory requirements, i.e. a short distance between the electrodesto prevent the discharge from being restarted after the current hasdropped to zero, and a large distance between the contact elements toensure resistance at high voltage. A suitable and economical compromisemust therefore be found between these two requirements and theinterrupter according to the present invention provides a novelcompromise of this nature.

This interrupter is characterized in that each of the said contactelements is provided with screening means that are electricallyconnected therewith and that are placed in such a manner as to separatefrom one another those of the interrupting gaps of said series which aredelimited by said contact elements and as to prevent any electrical ieldline to extend through more than one of these interrupting gaps.

The following description relates to two forms of embodiment, given byway of example, of the interrupter provided by the invention. It isillustrated by the accompanying drawing, in which:

FIG. 1 is a side view, partly in section, of the iirst form ofembodiment;

FIG. 2 is a section through part of the interrupter illustrated in FIG.l, with the interrupter shown in a rst particular position;

FIG. 3 is a similar section, with the interrupter shown in a secondparticular position;

FIG. 4 is an enlarged view of part of FIG. 3, illustrating the operationof the first form of embodiment;

FIGS. 5 to 9 are diagrams relating to various arrangements that someparts of this first form of embodiment can have;

FIGS. and 1l illustrate, partly in section, two variants ofthe firstform of embodiment;

FIG. 12 is a side view, partly in section, of the second form ofembodiment;

FIGS. 13 to 15 are partial sections of some elements visible in FIG. 12;

FIG. 16 shows on an enlarged scale a variant of a par of FIG. l2;

FIG. 17 shows, partly in section, like FIGS. 1 and 3, another variant ofthe rst embodiment;

FIG. 18 is a horizontal section along line XVIII-XVIII of FIG. 17;

FIG. 19 is a section like that of FIG. 16, of a variant similar to thatshown in FIG. 17 applied to the second embodiment.

In the example illustrated in FIG. l, the interrupter comprises afluidtight exhausted enclosure 1 which rests on a base 2 forming thebottom of the lower half 1b of the enclosure and into which enters via ailuidtight bellows sealing member 3 a conductive actuating rod 4 servingto operate the movable armature of the interrupter. This movablearmature is made up of a series of three circular metal shells 5, 6 and7, which are coaxially suspended on the actuating rod 4 one inside theother. These shells are isolated from each other by insulating spacers 8and 9 and, except for the outer shell 5, they are isolated from theactuating rod 4 by shoulders 10 and 11 formed in the spacers and by aninsulating washer 12 placed between the head 13 of the rod 4 and theinner shell 7. The shells 5, 6 and 7 and the insulating elements 8, 9and 12 are pressed against the head 13 by a nut 14 which at the sametime applies the outer shell 5 against the shoulder 15 of the rod 4 toensure electrical contact between the rod and the outer shell. The rod 4is uidtightly secured by a welding 16 to the top of the bellows 3 andthe latter is fastened to the upper half 1a of the enclosure 1 by awelding 17. The stationary armature of the interrupter is formed insimilar manner by a series of three metal shells 18, 19 and 20 which arecoaxially mounted inside each other and which are fixed to the base 2 bya threaded conductive rod 21. These shells are isolated from each otherand from the base 2 by insulating spacers 22, 23 and 24 and, except forthe inner shell 20, they are isolated from the threaded rod 21 byshoulders 25 and 26 formed in the spacers 22 and 23 respectively. Thethreaded rod 21 is moreover isolated from the base 2 by an insulatingwasher 27 having a shoulder 28. The inner shell 20 iS clamped beneaththe head 29 of the threaded rod 21 so as to be in electrical contactwith the latter. A nut 30 simultaneously to assemble together the shells18, 19 and 20 and the insulating elements 22, 23, 24 and 27, to ix thesecomponents to the base 2 and to ensure electrical contact between theinner shell 20 and the threaded rod 21. The base 2 carries a threadedstud 31 which is electrically connected thereto by a welding 32. The twohalves 1a and 1b of the enclosure 1 are secured to each other by awelding 33. The air contained in the enclosure 1 is removed through awithdrawal pipe 44 which, when the pressure reaches the lowest possiblevalue (of the order of 10*s torr and below), is sealed by nipping and ismade fluidtight by a welding 45. The threaded rod 21 acts as one of theterminals of the interrupter, which terminal has secured thereto by anut 34 a conductor 35, the latter thus being electrically connected tothe inner shell 20 of the stationary armature. The stud 31 acts as theother ternnnal of the interrupter and this terminal has secured theretoby a nut 36 a conductor 37, the latter thus being electrically connectedto the outer shell 5 of the movable armature.

Each of the armature carries a series of contact elements of circularshape around the axis 52 of the interrupter. The contact element of theouter shell 5 of the movable armature is shaped in the form of a crown38 laid ilat and projecting inwardly of the shell. lSimilarly, thecontact element of the inner shell 20 of the stationary armature isshaped in the form of a crown 39 laid ilat, but projecting outwardly ofthe shell. The contact elements of the other shells are formed bycircular components of T-shaped cross-section, alternately in upstandingand upside down positions. Thus, the shells 18 and 19 of the stationaryarmature have contact elements 40 and 41,

respectively, which are of inverted T cross-section, whereas the shells6 and 7 of the movable armature have contact elements 42 and 43,respectively, which are of upstanding T cross-section. 'Ihese circularcomponents are secured at the middle of their horizontal portions to theedges of their associated shells so that these horizontal portionsshould extend outwardly and inwardly of their associated shell. Thecontact elements are so sized that their horizontal portions 46 shouldoverlap each other so as to come into contact when the movable armatureis pressed against the stationary armature (closed position of theinterrupter, FIG. 2), while their vertical portions 47 form screenswhich prohibit any direct sighting between contiguous contact elements,even when the movable armature is moved away from the stationaryarmature (open position of the interrupter, FIG. 3). The displacementsof the movable armature are controlled by a mechanism not shown, whichoperates the actuating rod 4, the latter being axially movable inrelation to the enclosure 1 by virtue of the bellows sealing members 3.

When the various elements making up the interrupter are mounted in theenclosure 1 and once the latter is Huidtightly sealed along the ridge33, a high vacuum is created in the interrupter by connecting thewithdrawal pipe 44 to a high vacuum pumping unit with which a pressureof less than 10-8 torr can be obtained. While pumping is in progress,intensive degassing is performed, through heating, to reduce as far aspossible any subsequent degassing, either while the interrupter is instorage or while it is in use. As will be explained later the pressurein the enclosure 1 must not rise above a limit p1 defined by torr. cm.,the length d being that of the longest field line likely to appear inthe interrupter. That is why the pumping operation is carried on for aslong as the pressure does not reach a value of l-8 torr. Then thepressure becomes stabilized at this value, pumping is stopped, the pipe44 is nipped and sealed with welding. The pressure then slowly risesagain, as a result of a subsequent slow degassing action, but remainsbelow a value of the order of -4 torr.

The described interrupter operates as follows. Be it supposed that theinterrupter is closed 'with its contact elements occupying the positionsshown in FIG. 2. Then the movable armature moves away from thestationary armature and disengages the contact elements (FIG. 3), thevoltage across two contiguous contact elements is equal to the potentialdifference between the conductors 35 and 37 divided by the number ofinterrupting gaps appearing between the contact elements, i.e. by thetotal number of shells minus one (in the described example), there arethree shells (5, 6, 7) for the movable armature and three shells (18,19, 20) for the stationary armature, i.e. six in all, hence fiveinterruptions along the chain (38, 40, 42, 41, 43, 39). Because of thelow pressure in the enclosure this reduced voltage only produces adischarge of the diffuse are type, formed by several parallel conicalcolumns (termed Reece cones) Whose apexes are located on that one of thecontact elements which happens to be at negative potential in relationto its neighbour. Thus, supposing that the interruption takes place whenthe terminal 21 is possible in relation to the terminal 31, thepolarities are those indicated in FIG. 3. The diffuse arc dischargesthat come into being are as shown on an enlarged scale in FIG. 4 wherethe apexes 49 of the Reece cones 48 occurring in the interrupting gapbetween the horizontal portions of the contiguous contact elements 41and 43 are located on the contact element 41 whereas the Reece conesoccurring in the interrupting gap between the contiguous contactelements 42 and 41 are oppositely oriented, their apexes 51 beinglocated on the contact element 42. These apexes, which constitute heatconcentration points (cathodic spots), are highly mobile across thesurface of the corresponding contact elements and as a result do nocause much erosion of this surface. There is thus little vaporization ofthe cathode metal and the Reece cones contain only little vapour. Sincethe vacuum in the enclosure 1 is very high, there is besides thecathodic drop no other voltage between contiguous contact elements. Inparticular, there is no additional arc voltage due to collisions betweencharged particles (electrons or ions from the vapour of the cathodemetal) and residual gas molecules. Since, moreover, the residualpressure is such that the main free path of the electrons is greaterthan half of the largest distance lying between the interruptercomponents that are at different potentials, that any collisions withdual gas atomisor molecules could in no way cause an avalanche processto be initiated during the voltage rise which follows a currentinterruption. Consequently, dielectric restoration of the medium in thegaps where the discharges occur (i.e. between adjacent contact elements)takes place without difficulty as soon as the discharge current drops tozero. Because of this there is no restarting phenomenon.

Further, the vertical portions 47 of the intermediate contact elementsprevent any direct sighting from one interrupting space to another. Bythis is meant that the vertical portions firstly prevent a particle frompassing from one interrupting space to the next, this corresponding toprohibition of a direct sighting in the optical meaning of theexpression direct sighting, and secondly prevent field lines frompassing through more than one interrupting gap or join two non adjacentcontact elements, this corresponding to the electrical meaning of theexpression direct viewing. In this connection, besides the field lineswhich are located in the interrupting gap between two contiguous contactelements, like the field line 274 (FIG. 3), there may be field lineswhich join a contact element to the vertical portion of the adjacentcontact element, like the field line 275, or to the shell carrying thenext contact element of the same armature, like the field line 276.There could never be a field line such as the line 277 (drawn as a chainline) joining two non contiguous contact elements. Because of this, theinterrupting gaps can be regarded as independent as regards theirdielectric restoration.

As a result of this arrangement, firstly the dielectric restorationspeed of the interrupting gaps as a Iwhole is increased, since theindependence of these gaps makes it possible for the separaterestoration speeds therefor to be added together, and secondly thestatic value of the disruption voltage is increased since no field linecan pass through several potential jumps, this tending to reduce thefinal level of the restoration.

In other words, the described interrupter prevents the restartingphenomenon from occurring, improves resistance to disruption and reducesthe time taken to read this resistance to disruption.

The characteristic features of the described interrupter lie: in thefact that the interruption of the circuit is not localized, but isspread over several interruptions that give rise to a cascade of seriesmounted discharge paths; in the presence of bafiles which prevent directsighting from any one discharge path of a neighbouring discharge path;and in the presence of shells so arranged as to provide screensprohibiting the existence of long field lines or field lines causing alarge potential drop.

`In the form of embodiment that has just been described and which isdiagrammatically represented in FIG. 5, the baffles are simple insofaras each contact element, except for the terminal contact elements 55 and56, carries only one bafiie, this bale being symmetrically disposed inrelation to this element, as shown by the element 57 and its baffle 58which have been drawn in thicker lines. Other arrangements can beconceived, like that of FIG. 6 where the non terminal contact elementsare all identical and are provided, like the element '59, with a singlebaffle i60, this baffle being placed asymmetrically. FIGS. 7 and 8illustrate diagrammatically the case where some of the contact elementslike the elements 61 and 64, respectively, are provided with two baiiles62, 63 and 65, 66, respectively, whereas others, like the elements 67and 68, respectively, have none; in the case of FIG. 7, the baffles 62and 63 are symmetrically disposed on the element 61; in the case of FIG.8, the baffles l65 and 66 are asymmetrically disposed on the element 64.Finally, FIG. 9 shows the case where some elements, such as the element`69, are provided with three symmetrically disposed bailies, like thebailies 70, 71 and 72, whereas others, like the elements 73, have none.As will be appreciated, there are numerous possible variants as regardsthe number of baies, their location and their arrangement.

The interrupted illustrated in FIG. 1 comprises three contact elementsper armature, to wit the elements 38, 42 and 43 on the movable armatureand the elements 39, 40 and 41 on the stationary armature, thusproducing ve circuit interruptions. It will be clear that this number ofthree elements per armature is not imperative and that, according tocircumstances, for instance the power to be conveyed by the circuit andthe voltage, use can be made of a larger number of contact element,thereby splitting up to a greater extent the circuit interruptingaction.

It may be of advantage to increase the resiliency of the shells toenable the contact pressure to be more evenly distributed over theentire periphery of the contact elements. In such an event, it ispreferred to increase the diameter of the flat bottoms by giving theshells a cylindrical shape, as is shown in FIG. 10 in the case of theshells 74 and 75 of the movable armature and in the case of the shells76 and 77 of the stationary armature, instead of the frusto-conicalshells 5, 6, 7 and 18, 19, 20, respectively, visible in FIG. 1.

It may also be of advantage, still with a view to achieving a moreuniform distribution of the contact pressure, to split, at least in oneof the two armatures, one contact element into two parts with each partbeing supported by its own shell. This what is shown in FIG. 11 where itwill be seen now the contact part 7'8 of the stationary armature issplit into two parts 78a and 78b with each part being supported by itsown shell 78'a 78b, these two shells being connected to a common centralportion 78" so as to form a composite support for the split contactelement 78. Similarly, the contact element 79 of the stationary armatureis split into two parts 79a and 7912 which are supported by the shells79a and 79'b that are connected to a common central portion 79". Thisarrangement enables the two parts 78a and 78b to move in relation toeach other so that they can cooperate independently of one another withthe contiguous contact elements S3 and 255 of the movable armature. Thesame applies to the two parts 79a and 79b of the contact element 79which can thus cooperate independently of each other with the contiguouscontact elements 255 and 54 of the movable armature.

Of course, the T-shaped cross-section, Whether upstanding or inverted,of the contact elements in the interrupter illustrated in FIG. 1 is onlyone possibility among others and other cross-sections can be conceived,e.g. U-shaped, whether upstanding or inverted, with the limbs of one setbeing inserted between the limbs of the others. Some of the arrangementsdiscussed earlier in particular that which is diagrammaticallyillustrated in FIG. 1, are derived from shapes of this kind.

FIG. 12 illustrates a second form of embodiment in which the contactelements, instead of being distributed in a common plane, overincreasing diameters, as is the case with the first form of embodimentvisible in FIG. l, are axially distributed and have identical diameters.This interrupter comprises an enclosure 80 mounted on a base 81 andcapped by a cover 182, these elements being fluid tightly assembledtogether, as by welding.

The stationary armature comprises a stack of identical dishes 83 to 88which are separated from each other by insulating spacers `89 to 91 oftubular shape. These dishes have a radial cross-section as shown, on anenlarged scale, in FIG. 13. They are formed with a central limb 92having a rounded outline with the concave side thereof facing the axisof revolution 97, a at crown-shaped portion 93, a median groove 94, aconical portion 95 and a plane disc-shaped portion 96 which is placed ata level beneath that of the flat portion 93, to the same side thereof asthe groove 94. The distance between the limb 92 and the groove 94 issuch that the intervening space acts as a centering recess for receivingthe associated tubular spacer. Except for the outermost dishes 83 and88, the dishes within the stack are arranged in pairs, like the pair 84,and the pair 86, 87, and the two dishes of a pair are in invertedrelationship so that their central limbs 92 together constitute ananti-euvium screen of concave form, with the concave side facing theinside of the tube formed by the stack of spacers 89, and 91, and sothat the median groves 94 together constitute tield suppressing screenson the outside of this tube. The groove of the lowermost dish 183 capsan axial rim 98 provided at the centre of the base 81, inside theenclosure 80, whereas the groove of the uppermost dish 88 accommodates aclamping piece 99 which is welded to the top end of a clamping tube 100.This clamping tube is subjected to a pulling stress by means of a nut101 which is screwed onto a threaded member 102 fastened to the lowerpart of this tube. The nut 101 beats on a flat support 103 on which thebase 81 rests through the intermediary of a splined insulating sleeve104.

The movable armature comprises a series of three shells 105, 106 and 107which are formed by the outer portions of bell-shaped members having astheir axis of revolution the axis 97 of the interrupter. As shown byFIG. 14, which illustrates on an enlarged scale the prole of thesebells, each bell includes a flat central boss 108, a conical bottom 109which is connected to the central boss 108 by a conical flank 110, aninner peripheral boss 111, a flat crown-shaped portion 112, an outerperipheral boss 113, a connecting edge 114 and a conically ilaredskirt-shaped outer portion 115 which constitutes the shell mentionedearlier. The bells 116, 117 and 118 to which belong the shells 107, 106and 105 are fitted inside one another and are kept separate from eachother by insulating sleeves 119, 120 and 121, each sleeve bearing on thehat crownshaped portion of the associated bell (as shown by the chainline outline 122 in FIG. 14 from which may also be observed that thedistance between the peripheral bosses 111 and 113 is such that theintervening space acts as a centering recess for the associated sleeve).Between the bottoms of the bells 117 and 118 and the tops of the sleeves119 and 120, and on the top of the upper sleeve 121, are arrangedsupporting members 123, 124 and 125 having a profile as shown on anenlarged scale in FIG. l5. Each of these members is circularly shapedaround the axis 97 of the interrupter and comprises a flat central boss126, a conical flange 127 which is connected to the central boss 126 bya conical flank 128, an inner peripheral groove 129, a flat crown-shapedplate 130, and an outer peripheral groove 131, the distance betweenthese peripheral grooves being such that the intervening space acts as acentering recess for a sleeve, as shown by the chain line outline 132.The dimensions of these various parts and their conicities are such thatthe supporting members t exactly against the bottoms of the associatedbells, so that the fitting of the peripheral grooves 129 and 131 in thesupporting members with the peripheral bosses 111 and 113 in the bellsforms two field suppressing screens located on opposite sides of thejunction between two consecutive insulating sleeves, as will be observedfrom FIG. 12 as regards the supporting members 124 and the bell 118. Thelower supporting member 116 rests, through the intermediary of a centralspacer 133, on an auxiliary shell 134 having a conical ange 135 which isparallel to the ange of this supporting member, and a conical skirt 136which is parallel to the skirt of the inner bell '7. The hub of thisauxiliary shell 134 comprises a central portion 137 surrounded by acrown 138. The central portion 137 is secured to the top end of anactuating rod 139, made of metal or other material, which is housedinside the clamping tube 100, its diameter being such as not to touchthis tube. The crown 138 is connected, through the intermediary of afluidtight bellows 140, to the clamping piece 99, this connection beingeffected in iluidtight manner, by welding at each end of the bellows140. The upper supporting member 125 bears on a dished member 141 havinga rim 142 and a central stud 143. The rim 142 is connected, through theintermediary of a fluidtight bellows 144, to the cover 82, thisconnection being effected in fluidtight manner, by welding at each endof the bellows 144. The central stud 1143 slides in a recess 145 formedin a threaded stopper 146 which is in turn accommodated in a threadedhole 147 in the cover 82. A spring 148 is prestressed between thestopper 146 and the bottom of the dished member 141.

Finally, the clamping piece 99 is welded to a glass tube 1149 whichsurrounds the clamping tube 100 and which is terminated at its lower endby a pleated folded-back sleeve 150. This sleeve, in which the pleatsare only made to provide for heat expansion, is welded to the lower endof a uidtight metal bellows 151 whose top end is tluidtightly connectedto the base 81 of the interrupter. The glassmetal welding 152 issurrounded by a peripheral screening hood 153 having an inner part 154and an outer part 155.

The contact elements carried by the stationary and movable armatures aredistributed in three identical superposed stages 156, 157 and 158, eachof which is constructed as shown on an enlarged scale in FIG. 16. Eachstage, e.g. stage 156, comprises a part 159 which is attached to themovable armature, and two parts, 160 and 161, which are attached to thestationary part. Each of these parts is of circularly symmetricalcross-section about the axis 97 of the interrupter. In cross-section themember 159 which is `attached to the movable armature is shaped like anasymmetrical inverted U with unequal limbs 162 and 163, the longer limb162 being remote from the axis 97 and the shorter limb being closer tothis axis. The longer limb 1-62 of this member 159 extends into theperipheral channel formed by the first, 160, of the two members whichare attached to the stationary armature, the cross-section of this firstmember being shaped like an asymmetrical U having a longer limb 164remote from the axis and a shorter limb 165 nearer the axis. The shorterlimb 163 of the member 159 extends into the peripheral channel formed bythe second, 161, of the two members which are attached to the stationaryarmature, the cross-section of this second member being shaped like anasymmetrical U having a shorter limb 166 remote from the axis and alonger limb 167 nearer the axis, this longer limb being extendeddownwards by an appendage 168. The members 159, 160 and 161 eachcomprise a fastening rim 169, 170 and 171, respectively, by means ofwhich it is fastened to the associated armature. Thus, the member 159 ofstage 156 is fastened by the fastening rim 169 to the tip of the shell105, the member 160 of this selfsame stage is attached by the fasteningrim 170 to the plane portion 9683 of the dish 83 and the member 161 isattached by the fastening rim 171 to the plane portion 9684 of the dish84. When the interrupter is closed, the electrical connection betweenthe contact elements of the stage 1516 is established via the bottom 172of the peripheral channel formed by the member 160, the tip 173 of theouter edge 162 of the inverted peripheral channel formed by the member159, the tip 174 of the inner edge 163 of this selfsame channel and thebottom 175 of the peripheral channel formed by the member 161. This iswhat is shown by the chain line outlines visible in FIG. 16. There isthus set up, at the level of the stage 1516, an electrical connectionbetween the dishes 83 and 84 of the stationary armature; at the level ofthe stage 157, an electrical connection between the dishes and 86 ofthis selfsame stationary armature; and, at the level of the stage 158,an electrical connection between the dishes 87 and 88 again of thisselfsame stationary armature. Since the dishes 84 and 85, on the onehand, and 86 and 87, on the other hand, are in electrical contact witheach other, and since the lowermost dish 83 is in electrical contactwith the base 81, and the uppermost dish 88 is in electrical contactwith the clamping tube 100 through the intermediary of the clampingpiece 99, and the clamping tube is in electrical contact with thesupport 103 through the intermediary of the member 102 and of the nut101, it will be apparent that, in the closed position of theinterrupter, the latter sets up an electrical connection between thebase 81 and the support 103. It is therefore to these latter parts thatare connected the terminals 176 and 177 by vmeans of which theinterrupter is connected to the current supply cables 178 and 179,respectively. To afvoid having current flowing through the threads ofthe nut 101 and of the member 10.2, there is provided an arm 180 whichestablishes a direct electrical connection between the support 103 andthe clamping tube 100.

It will be apparent that there is a similarity between this interrupterand the one described with reference to FIG. 1l: the members 159belonging to the stages 156, 157 and 158 (FIG. l2) constitute thecontact elements of the movable armature, whereas the lower U-shapedmembers belonging to one stage (e.g. the U-shaped member 16011 of thestage 157) and the upper U-shaped members belonging to the sub-jacentstage (e.g. the U-shaped member 161 of the stage 156) constitute the twoparts of split contact elements of the stationary armature, the dishesto which are secured these members (c g. the dishes 87 and 86 and thedishes 85 and 84, respectively) constituting the associated compositesupports.

The operation of this second form of embodiment is in respects similarto that of the first form of embodiment illustrated in FIG. l. The edges164 and 165 (FIG. 16) of the peripheral channel formed by the part 160and the edges 166 and 167 of the peripheral channel formed by the part161 constitute within any one stage the baffles that prevent directsighting of one interrupting gap from another, e.g. of the interruptinggap 182 from the interrupting gap 181 in the stage 156 illustrated inthis ligure. The same applies to the other stages 157 and 158 (FIG. 12).However, the cylindrical screen which has as its cross-section theappendage 168 (FIG. 16) of the longer limb 167 of the part 1161 of stage156, as also the analogous screens in the other stages do not exist inFIG. 1: these are so-called anti-vapour screens for preventing thevapour generated by the discharge in the interruption gaps 181 and 182from diusing within the enclosure 80. As for the auxiliary shell 134, itsimultaneously constitutes, firstly, another, additional, anti-vapourscreen and, secondly, an additional baflie for preventing directsighting between the clamping piece 99 and the inner shell 107.

As explained earlier the nut 101 serves to clamp the members making upthe stationary armature and to iix them to the support 103 and to thebase 81. As for the threaded stopper 146 it serves to adjust theprestressing of the spring 148, this spring urging the movable armatureagainst the stationary armature. It is therefore this spring whichexerts the contacting pressure between the contact elements of thestages 156 to 158 and it is against the action of this spring that theactuating rod 139 has to be moved when it is required to separate thecontact elements upon opening the interrupter.

It will be apparent that this second form of embodiment has theadvantage, in relation to the first, of being produced from a limitednumber of standard parts, thereby reducing the number of machiningoperations. The dishes 83 to 88 are identical and are easily made bystamping. The contact elements of the various stages only comprise threetypes of diiferent parts, i.e. the parts 159, 160 and 161, which partsonly differ from one stage to the next as regards the diameter of theirfastening rims 169, 170 and 171, respectively. Simple lathe operationswill easily impart to these diameters the values they are required tohave in the stages for which they are intended. The bells :5, 106 and107 are all identical as regards their profile, which profile is verywell suited to production by stamping. Only the length of their skirts115 (FIG. 414) changes from one bell to the next so that they can all bederived from the longest such bell, i.e. the outer bell 118, by simpleremoval of the excess length. The supporting members 123i, 124 and 125are all identical and are designed to be produced by stamping. Further,the arrangement that has been adopted makes it possible to modify to alarge extent the number of interrupting gaps without having to resort tonew parts: it suiiices to increase the number of stacked stages; thisadds to the length of the interrupter without substantially modifyingits diameter.

It should be pointed out that the arrangement that has been adopted forthis second form of embodiment avoids having to expose to the vacuum forno good purpose purely mechanical components. Thus the clamping spring148 and the device 146, 147 for modifying its prestressing are locatedoutside the exhausted enclosure 80. The same applies to the clampingdevice of the stationary armature, i.e. the nut 101, the member 102 andthe tube 1100. Moreover, the actuating rod 139 is not subjected to anypull: it only operates on a thrust basis against the action of the forceexerted by the spring 148 so that even when the switch is closed itremains subjected to a compressive force and never to a pulling force.

Finally, it will be observed that in this interrupter the terminals 176and 177 are both electrically connected to the stationary armature only,i.e. to the extreme contact elements thereof, the movable armature notbeing connected to any terminal.

Of course, either of the two described forms of embodiment can beequipped with the discharge confinement device called cathodic barrierand described in Swiss patent application No. 17,52'6/70. This is whatis diagrammatically illustrated in FIG. 16 in which are to be seen, forthe purpose of confining the discharge within the interrupting gap 181,the annular cathodic barriers 184 and 185 provided on the part 160 andthe cathodic barriers 186 and 187 provided on the contact element 159,and, for the purpose of confining the discharge in the interrupting gapi182, the annular cathodic barriers 188 and 1-89 provided on the contactelement 159 and the cathodic barriers 190 and 191 provided on the part161.

Furthermore, it may be of advantage to provide the screened contactelements, like the element 159 (FIG. 16) of the stage 156 (the latterbeing screened by virtue of the fact that its flanges 162 and 163` aretrapped in the peripheral channels i116() and 161, respectively), withhelicoidal slots like the slots 195 formed on the outer flange 162, andlike the slots 196 formed on the inner flange 163 of this contactelement 159. As is known in conventional interrupters, such anarrangement brings about rapid displacement of the discharge impactpoints along the helicoidal petals dened by these slots in the contactelement, like the petal 197 or the peta 198i. This displacement helps tospread the heating action due to the discharges and limits erosion ofthe contact surfaces and hence vaporization of the metal from which areare made. These helicoidal slots, however, must not reach the cathodicbarriers 186, 1-87 and 1818, 189, respectively, otherwise theeffectiveness of the latter would be adversely affected.

Since the purpose of cutting up the -llanges into petals is to channelthe current owing in the contact elements along helicoidal paths, asimilar, although less marked, eifect can be obtained by forming onthese contact elements grooves instead of slots, the presence of thesegrooves having the effect of locally increasing by a nite amount theelectrical resistance of these contact elements whereas that of theslots renders such an increase infinite. These resistance increasinggrooves, which, in pairs, define petals along which the current ischanneled, can be formed on the flanges 166 and 167 and on the bottom175 of the part 161, as well as on the flanges 164 and 1165 and on thebottom 172 of the part 160. They are preferably formed on the surfacesof these parts lying opposite the surfaces between which the dischargestake place. Along these surfaces they have helicoidal or spiral outlinessuch that the current being channelled by these grooves sets up amagnetic field having a component capable of causing the discharge totravel along the contact elements in a circular translationary movementcentered on the axis 97 of these elements.

A similar arrangement can be provided in the interrupter of FIG. l. Forthis, the grooves are formed in the surfaces of the contact elementslying opposite the bafes (or screening flanges) 47. Thus referring toFIG. 4, the grooves are formed on the underneath surface of the element41 and on the top surfaces of the elements 42 and 43.

In connection 'with the arrangements illustrated in FIGS. l0 and 1l, itshould be noted that the added flexibility that they impart to thearmatures can in some cases be bothersome for the movable armature sinceit increases its vibrational tendencies. in such cases, it is preferredto stick to shells of conical shape for the movable armature, like theshells 5, 6 and 7 in FIG. 1, and to use ilexible shells like the shells76 and 77 (FIG. l0) or 78'a, 78b, 78" and 79'a, 79'b, 79" (FIG. 11) onlyfor the stationary armature.

In either of the above described embodiments of the vacuum interrupterthe discharge that occurs when it is opened does not restart once thecurrent has passed through zero during the alternation change thatfollows this opening action. This result is achieved by providing thecontact elements, besides the small spacing made possible by resortingto several of such elements to dene a plurality of interrupting gapsarranged in series, with an extensive contact area and by arrangingbetween adjacent interrupting gaps screens which render the latterelectrically independent from one another. These steps create conditionswhich prevent discharges generated in the interrupting gaps from passingfrom diffuse arc flow conditions to single column flow conditions andwhich as a result stop these discharges from restarting once thecurrent, as it alternates, crosses the iirst zero crossing point afteropening the interrupter.

This however is only true in so far as the discharges occur without failunder diffuse arc conditions when the interrupter is opened. The variantthat will now be described, and that applies to either of the precedingembodiments, to reduce the risk of having discharges occurring undercolumn flow conditions.

It will be recalled that, according to the Mitchell theory, transitionfrom diluse arc ow conditions (characterized by the existence inparallel of several highly mobile elementary discharges, called Reececones) to column flow conditions (characterized by a single concentratedarc having little mobility) results from instabilities of the diffuse owconditions that occur when the inter-electrode voltage exceeds 40 'v.Since this voltage is the sum of a cathodic voltage of 20 v. (in theimmediate vicinity of the cathode) and of an ohmic drop RI within theplasma existing in the space lying between contact elements, this ohmicdrop RI must be kept below 20 V. to prevent transition. If the contactelements are provided with an extensive area S and if their spacing d iskept small, the resistance R can be lowered according to the known lawR=k d/S which applies whenever the cones are sufficiently numerous tooverlap one another partly. In other words, to prevent transitionbetween diffuse flow conditions and column flow conditions, the valueS/d must be made as high as possible for each of the interrupting gaps.This is what the above described forms of interrupter achieve.

But when the discharge is started, i.e. as the contact elements begin tomove apart, there is formed a bridge of liquefied metal; this bridge isprogressively drawn out and finally bursts. Thus, for a brief period oftime after the burst, there is a transitory stage during which thecontact elements continue to move apart until they reach maximum spacingcorresponding to the open state of the interrupter. During thistransitory state, the instantaneous value S/d varies greatly and to anextend in no way related to the final value corresponding to the openstate, and it may happen that, before even the Reece cones have beenable to disperse, the current exceeds the critical value (of the orderof ka. in the case of contact elements made of copper) that enables asingle column to be formed. The contact elements should therefore beadapted so as to prevent without fail the current from reaching duringthe transitory state the critical value that leads to the formation of asingle column, in other words be adapted to start, between the pairs ofcontact elements being moved apart, a plurality of discharges underdiffuse fiow conditions with the current having to flow in theinterrupting gaps set up between these Contact elements being divided upbetween them. Technically this amounts to increasing the simultaneity ofthe breaking action between all points of the two contact elements beingmoved apart, whilst maintaining a high pressure at all of these pointswhen the contact elements are in contact in the closed position of theinterrupter. This is what is achieved by the variants depicted in FIGS.17 and 18 in relation to the first embodiment, and in FIG. 19, inrelation to the second embodiment, it being assumed that one of the twoarmatures is movable and the other is stationary.

In the variant illustrated in FIGS. 17 and 18, the contact elements ofthe stationary armature are splitting by cutting therein radial slots,such as the slots 239 in the case of the contact element 39, the slots240 in the case of the contact element 40 and the slots 241 in the caseof the contact element 41. In this way, each Contact element fractionforms the tip of a contact fingen Thus, the fractions 339 of the contactelement 39 form the tips of contact fingers 220. The same applies to thefractions 340 of contact element 40, `which form the tips of fingers218, and to the fractions 341 of contact ele ment 41 which form the tipsof lingers 219. This arrangement imparts to the adjacent fractions ofany one contact element an individual -fiexiblity which endows them withsome mobility in relation to each other, such mobility multiplying,-when the interrupter is in the closed position, the points at which astationary contact element touches the two movable contact elements thatare adjacent thereto and with which it cooperates: it is then eachfraction which touches, individually, these two contact elements. As aresult, the machining tolerances may be less tight and the heatingaction due to current throughfiow is better distributed and less large.

The mobility of each finger in relation to its neighbours is all thegreater when the radial slots are deep. But a greater mobility isaccompanied by a reduction of the force with which each fraction touchesthe or each contiguous movable contact elements. This is a drawbackbecause the force with which each fraction is applied against themovable contact element with which it cooperates must be sufiicient toavoid, firstly, any resistive welding tending to attach this fraction tothis contact element and, secondly, any separation of the contacts by amagnetic bouncing effect. A suitable compromise must therefore be foundbetween the fiexibility of the fingers and the force they exert when theinterrupter is closed. This compromise, which rests on staticconsiderations, determines the depth to which the radial slots mustextend into the corresponding shells 18, 19 and 20, and defines theradii R1, R2 and R3 reached by their bottoms. These parameters can becalculated in an approximate way but their definite values aredetermined by empiric tests.

The splitting up of the stationary contact elements has anotheradvantage which is most important when the armature is being opened: itis that the extra breaking current that springs between the contactelements when the latter are being separated is distributed betweenseveral parallel partial discharges, with at least one per finger, sothat each only conveys a limited amount of current. If the current ateach discharge starting point does not exceed a limiting value (of theorder of 5 ka. in the case of contact elements made of copper), thecorresponding discharges are bound to start up in diffuse arc form. Thishowever supposes that each of the fractions into which the stationarycontact elements are divided separate simultaneously. In thisconnection, if one fraction separates from its movable contact elementbefore the others, the current it was conveying before this separationoccurred produces, by a self-inductance effect, a discharge which,because it is short-circuited by the fractions that have not yetseparated, only lasts for as long as this self-inductance effect iscapable of maintaining, between this fraction and the correspondingmobile contact element, the minimum voltage of 20 v. representing thecathodic drop within this discharge. This length of time, which is veryshort since it does not exceed a few microseconds, represents themaximum time lag that may be tolerated for the separation between thefirst and last fractions to open of one stationary contact element: itthus defines the simultaneity with which these fractions must beseparated from the corresponding movable contact element. In practice,during this time lag, the fingers must not be allowed time to follow themovable contact element in its breaking movement. This amounts to givingto the mass of the various fractions and to the elasticity of thecorresponding fingers values such that the vibration period of thesefingers is much greater than the time taken by the movable contactelement to move away therefrom.

These dynamic considerations, which are of the greatest importance, mustbe taken into account when reaching the compromise that determines thedepth of the slots. They involve, 'besides the elasticity of thematerial used for the shells 39, 40, 41 of the movable armaturesuchelasticity governing the fiexibility of each finger-the suspended massconstituted by the mass of the contact element fraction forming the tipof this finger. Here again, the depth of the slots and the mass of thecontact element fractions carried by the fingers are adjusted byempirical tests.

As is apparent from FIG. 18, the fingers of one shell can be angularlyoffset in relation to the fingers of another shell: thus the fingers 218formed in the outer shell 18 are angularly offset by half a width inrelation to the fingers 219 formed in the shell 19. Also, the angularwidth of the fingers of one shell is not necessarily equal to theangular width of the fingers of another shell: if the fingers 218 havethe same angular width as the ngers 2119, the fingers 220 of the innershell 20 have a double angular width.

If the interrupter has contact elements in the form of annuli stacked ontop of each other into a substantially cylindrical tubular structure,like that shown in FIG. 12,. the splitting up of the stationary contactelements leads to the arrangement shown in FIG. 19. It will be observedfrom the latter, which must be compared with FIG. 16, how the radialslots formed on the contact elements are arranged. Thus the annulus isprovided with radial slots of which may be seen the portions 251 locatedon its outer flank 1164, the portions 252 on its inner flange 1165 andthe portions 253 located on its mounting annulus '170. The annulus 161is also provided with radial slots of which may be seen the portions 261located on its outer lflange 166, the portions 262 located on its innerliange '167 and the portions 263 located on its mounting annulus 171. Inthis way, each of the stationary annuli 160, 161 belonging to one stage(here stage 156) is split up into sections which form the tips ofcontact fingers, such as the lingers 270 in the case of the annulus 1-60and the lingers 271 in the case of the annulus 161.

Obviously the splitting up of the stationary contact elements intofingers 270, `271 in no way prevents the movable contact elements frombeing divided into petals by helical slots, as described above and as isapparent from FIG. 19 in the case of the movable contact element 159which is divided into petals 197, 198 by helical slots 195, 196.

Since the elasticity of the contact fingers might be the cause ofbouncing when the interrupter is being closed, it may be of advantage toprovide means capable of preventing this phenomenon from occurring. Thisis what is shown in FIG. 19, where the bottoms of the grooves 172, 175of the contact elements 160, 161, respectively, are each defined byoblique surfaces 280, 281, respectively, which form bevels into whichextend the tips 173, 174 of the flanks 162 and 163, respectively, of themovable contact element 159. The presence of these bevels has the electof preventing any bouncing of the lingers 270, 271 when the interrupteris being closed, the friction of the tips '173, 174 against the surfaces280, 281 absorbing the energy that would cause such bouncing.

If for reasons of simplicity the cathodic barriers appearing in FIG. 116have not been shown in FIG. 19, clearly there is nothing to stop thestationary contact members that are split up into ngers from being soprovided.

We claim:

r1. A vacuum single-pole interrupter for alternating electric current,having a plurality of contact elements operating in series, said contactelements belonging to irst and second contact armatures capable ofmoving in relation to each other along an axis of displacement, thecontact elements of one armature cooperating with those of the otherarmature so as together to form a chain of contact elementsconstituting, when the interrupter is closed, a conduction pathalternately passing through the contact elements of said two armaturesand forming, when the interrupter is open, a series of interrupting gapsalternately defined 'by said contact, the outermost two elements of thischain being electrically connected to the rst and second, respectively,of a pair of terminals serving to connect the interrupter to an electricnetwork, characterized in that each of said contact elements is providedwith screening means which are electrically connected therewith andwhich are arranged so as to separate from each other those interruptinggaps which, within said series, are defined by this contact element andso as to prevent any one electric field line from extending through morethan one of these interrupting gaps.

2. An intrrupter according to claim f1, characterized in that each ofthe said contact elements consists of a circular conductive crown whichhas at least one annular contacting surface and which is located at theperiphery of a round conductive support, at least one of the crowns ofat least one of the two armatures being provided with at least one dangesubstantially at right angles to the contacting surface of said crown,and the supports bearing the crowns of at least one of said armatureshaving a concave shape enabling them to fit into one another, in thatwithin each of said armatures the supports are arranged in coaxialpositions, that are aligned along said axis of displacement, and areattached to each other by fastening means which isolate themelectrically from one another, the flanges being in all of the crowns ofthis armature oriented in a common direction, and in that, within anyone armature, the concave supports are tted into each other, thearrangement being such that, when the interrupter is closed, the contactsurfaces borne by the crowns of one armature are pressed against thehomologous contact surfaces borne by the crowns of the other armaturethus foming said conduction path, and that, when the interrupter isopen, the contact surfaces bome by the crowns of one armature areseparated from the homologous contact surfaces 'borne by the crowns ofthe other armature thus forming said series of interrupting gaps, theflanges and the supports of these crowns together forming said screeningmeans.

3. An interrupter according to claim 2, characterized in that saidcrowns are concentric crowns of increasing diameters arranged one withinthe other and alternately belonging to one then the other of saidarmatures, said crowns together forming a substantially plane annularstructure at right angles to said axis of displacement.

4. An interrupter according to claim 2, characterized in that saidcrowns are coaxial crowns of substantially equal diameters which arestacked one above the other and which alternately belong to one then theother of said armatures, said crowns together forming a substantiallycylindrical tubular structure coaxial with said axis of displacement.

5. An interrupter according to claim 2, characterized in that the saidoutermost two elements of said chain belong to different armatures,whereby the interrupter may be connected to the network through theintermediary of these two armatures.

6. An interrupter according to claim 2, characterized in that the saidoutermost two elements of said chain belong to one armature, whereby theinterrupter may be connected to the network through the intermediary ofthis one armature.

7. An interrupter according to claim 2, characterized in that each ofsaid armatures includes at least one crown having at least one of saidflanges.

8. An interrupter according to claim 2, characterized in that the crownsof one of said armatures each have at least two flanges and in that thecrowns of the other armature have no anges.

9. An interrupter according to claim 2, characterized in that, withineach of said armatures, crowns having at least one flange alternate withcrowns having no flanges.

10. An interrupter according to claim 2, characterized in that, withinat least one of the armatures, at least one of said crowns is split intotwo concentric parts of which one includes one of the contact surfacesof this crown and is secured to the edge of a first circular member, andof which the other includes the other contact surface of this crown andis secured to the edge of a second circular member, said two circularmembers being connected to each other at the central portions thereof soas together to form a composite support enabling relative movement ofone of the contact surfaces of said crown in relation to the other.

11. An interrupter according to claim 3, characterized in that thecross-section of each of said concentric crowns is shaped like a T lyingthe right way up in the case of the crowns of one of said armatures andupside down in the case of the crowns of the other armature, the limb ofthis T constituting the cross-section of the ange of said crown.

12. An interrupter according to claim 4, characterized in that thecross-section of each of the coaxial crowns of the lirst of saidarmatures is shaped like two superposed Us, the bottoms of these Usrespectively constituting the cross-section of either of the two contactsurfaces of this crown and the limbs of these Us forming thecross-section of each of two pairs of flanges, with one pair encirclingone of said contact surfaces and with the other pair encircling theother contact surface, and in that the crosssection of each of thecoaxial crowns of the second of said armatures is shaped like aninverted U having unequal limbs, the ends of these limbs respectivelyconstituting the cross-sections of either of the two contact surfaces ofthis crown, said crowns being so arranged that the limbs of the invertedU of the cross-section of the crown of the second armature extend intothe respective Us of the cross-sections of the crowns of the rstarmature.

13. An interrupter according to claim 12, characterized in that thecrowns of said first armature are split into two parts of which one hasas its cross-section one of said Us and of which the other has as itscross-section the other of said Us, each of these parts being secured tothe edge of a member shaped like a wide-brimmed dish, these dishes beingassembled back to back so as to constitute a composite support.

14. An interrupter according to claim 12, characterized in that thesupports of the crowns of said second armature are shaped like conicalbells all having the same meridian profile, these conical bells beingfitted into each other and being kept electrically isolated from eachother by insulating spacers which maintain their bottoms equidistantfrom one another, and each of the crowns of this second armature havingan outer peripheral limb by means of which this crown is secured to theedge of the associated bell.

15. An interrupter according to claim 2, characterized in that saidcontact elements are provided with cathodic barriers so arranged as todelimit the contact surfaces of each said element.

16. An interrupter according to claim 1, characterized in that someportions at least of said contact elements are provided with lines alongwhich the resistance oiered to electric current flow is increased, pairsof said lines delimiting in said portions paths of lesser resistancewhich channel the electrical current flowing therein, the shape of theselines being so selected that the electromagnetic action exerted by thiscurrent on the discharges occurring in said interruption gaps willimpart to these dischargers a circular translationary movement alongthese contact elements.

17. An interrupter according to claim 16, characterized in that saidlines of increased resistance are formed by grooves.

18. An interrupter according to claim 16, characterized in that saidlines of increased resistance are formed by slots.

19. An interrupter according to claim 1, characterized in that one ofsaid armatures is a stationary armature of which each contact elementconsists of a plurality of sections which are attached to this armatureby elastic elements that render these sections movable in relation toeach other in planes passing through said axis of displacement, the massof these sections and the elasticity of these elastic elements beingchosen so that when the interrupter is closed each of the sectionedcontact elements of the stationary armature touches each of thecorresponding contact elements of the other armature at at least onepoint per section, and so that when the interrupter opens the inertia ofthese sections prevents them from accompanying the contact elements ofthe other armature while they are moving away.

20. An interrupter according to claim 19, characterized in that each ofthe sections belonging to one Contact element of said stationaryarmature has the shape of an annulus sector, each of these sectors beingsecured to the tip of a radial finger consisting of the portion of saidround support lying between two adjacent slots belonging to a pluralityof meridian slots formed in said support from its outer edge, the axisof said support corresponding to said displacement axis and said radialfingers constituting said elastic elements, the flexibility of saidlingers being determined by the radial depth of the slots.

21. An interrupter according to claim 20, characterized in that the massof said sections and the radial depth of said meridian slots are soselected that the natural period of the exing vibrations of each of saidlingers in the axial direction is greater than the time taken by thecontact elements of the movable armature to move away from the contactelements formed by said sections.

22. An interrupter according to claim 19, characterized in that at leastone of the two surfaces along which two cooperating contact elementscontact each other when the interrupter is closed is oblique in relationto said axis of displacement thereby to increase the friction of thesurfaces against each other and to prevent said contact elements frombouncing.

References Cited UNITED STATES PATENTS 2,976,382 3/1961 Lee 200-144 B3,211,866 10/1965 Crouch et al. 200`l44 B 3,244,843 4/ 1966 Ross 200-144B FOREIGN PATENTS 1,389,836 1/1965 France 200-l44 B 1,145,151 3/1969Great Britain 200--144 B 1,901,067 10/1969 Germany 200--144 B ROBERT S.MACON, Primary Examiner U.S. c1. xn.l 20o- 166 o Dedication3,705,144.-Perre Genequand, Geneva, Switzerland. VACUUM INTERRUPT-v EROR SWITCH FOR ELECTRIC POWER NETWORKS. Patent dated Dec. 5, 1972.Dedication filed Mar. 26, 1984, by the assignee, Battelle MemorialInstitute. Hereby dedicates to the People of the United States theentire remaining term of said patent.

[Official Gazette May 29, 1984.]

Dedication 3,705,144.-Perre Genequand, Geneva, Switzerland. VACUUMINTERRUPT- ER OR SWITCH FOR ELECTRIC POWER NETWORKS. Patent dated Dec.5, 1972. Dedication filed Mar. 26, 1984, by the assignee, BattelleMemorial Institute.

Hereby dedicates to the People of the United States the entire remainingterm of said patent.

[Official Gazette May 29, 1984.]

